Abstract
This paper presents the broadband antenna for the microwave radiometric sensing of internal body temperature. For broadband operation, the bow-tie antenna was designed and backed with a cylindrical cavity, which decreased environmental electromagnetic interference and also improved the directivity of the antenna. The broadband impedance-transforming balun in microstrip form was also designed to feed the bow-tie antenna, and was located inside the cavity. An impedance-matching dielectric layer (IMDL) was introduced on top of the bow-tie antenna, for impedance match with the human body with high permittivity. The fabricated antenna was measured in free space with the IMDL removed, showing an input reflection coefficient lower than −10 dB from 2.64 to > 3.60 GHz with antenna gain over 6.0 dBi and radiation efficiency over 74.7% from 2.7 to 3.5 GHz. The IMDL was re-installed on the cavity-backed bow-tie antenna to measure the antenna performance for the human head with relative permittivity of about 40. The measured reflection coefficient was as low as −28.9 dB at 2.95 GHz and lower than −10 dB from 2.65 to > 3.5 GHz. It was also shown that the designed antenna recovered a good impedance match by adjusting the permittivity and thickness of the IMDL for the different parts of the human body with different permittivities.
Highlights
Microwave frequencies in the low GHz range allow good penetration of human tissues and high image resolutions
Ultra-wideband (UWB) microwave signals are illuminated in the human body, and the reflected waves are collected by broadband antenna to image and detect malignant tissues in breast cancer detection [2]
We present the cavity-backed bow-tie antenna with broadband impedance- matching with the human body, high directivity, and good shielding capability for the radiometric sensing of internal body temperature
Summary
Microwave frequencies in the low GHz range allow good penetration of human tissues and high image resolutions. In [6], a non-contact radiometer, using the cavity-backed slot antenna, was introduced at 1.4 GHz to monitor the core body temperature. We present the cavity-backed bow-tie antenna with broadband impedance- matching with the human body, high directivity, and good shielding capability for the radiometric sensing of internal body temperature. For this purpose, the bow-tie patch was adopted as a basic radiating element with broadband performance. The impedance-matching dielectric layer (IMDL) was introduced on top of the bow-tie patch, to reduce the wave reflections from the human body with high permittivity, and to allow physical and thermal isolation of the antenna from the human body.
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